Frequency changing



Oct. 22, RI R RIESZ FREQUENCY CHANGING Filed Jane so, 1939 R V my E N .H VR m m WR. N al w l I R v. un .o Ih @S B 90 n @n mm C Q Nw R N\ n: Imm, @SS emaux Q. uo mm, .n m Nh Q QN u v om N m, QN uit hm, m 53M bv mm NQRNW v V Suv? xv Mm o. M l l f a Y REN M, .9.90 QWPKUWQ w .w w 5r Il SN 1 Iv W 0 bmw b Oct. 22, '1940. R. R. RlEsz FREQUENCY CHANGING Filed June 30, 1939 5 Sheetjs-=$heet- 2.

n wu

Z ws n TF. N Nl .R wh. m WR T R. p. A VM B Al. QSE. Qvb.

Oct. 22, 1940.

R. R. RlEsz 2,219,021

l FREQUENCY yCHANGING Filed June 30, 1939 5 Sheets-Sheet 3 C ONDUC T/NG PL UGS NSULATING MA TER/AL R. l?. RESZ BV M5 ATTO NEV quenyrangef Another object is to electrostatically record signal variations ata givenrate, andvto repro-YA Patented Oct. 22, 1940 l UNITED STATES vParlant1*torries;]

- I FREQUENCY CHANGING f y Robert rR. Riesz, Mount Ver-non, N. Yf, assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation 'of New York Application June 3o, 1939,'seria1N0..zs2,021

11 Claims.

f This invention relates to frequency' changers and particularly to frequency changers employing. electrostatic recorders and reproducers..

An object of the invention is to change the n' 5 frequency range of Van alternating current sigthe, frequency range of an alternating current signal wave prior 'to transmitting it over a sig-l Y naling path, and at a receivingpoint to expand the received wave to restore it to its original freduce the recordedA variations at a different rate. These objects are attained inv accordancevwith the' invention by the use of lspecially designed cathode ray electrostatic recording and. reproducing devices at the sending and receiving ysta-Y tions of va signaling system, for example, a speech 2liv Wave signaling system.` Inl one embodiment,4 a

` cathode V,ray electrostatic recording and reproy ducing device at the sending station operatesI to chop up an alternating current Wave representing speech or other signalsA of a periodic'character .to'

beftransmtted, into a series jof'equal shorty elements on a time .basis they time intervalv of chopping being equalto the fundamental period ofthe original signal or an integral multiple orsubmultiple thereof, to eliminate alternate signal maining elements on a time scale so as to. double their duration and thus effectively to vhalve .the

total signal frequency range. .The signal .Wave so modified is transmitted over a signal transmission line, and at the .receiving station two similar cathode rayA devices operate alternately toreproduce each of the received signal elements at twice the speed atwhich it is received sothatl .each'frequency therein is restored to its original value, the two reproduced portions of each .sig-

elements of the Waves and to stretch outthe re.

.nal segment being laid down side by side so that shows a plan View' of the target. 'Referring to (Cl. ITS- 44) .A l Figs. 3 and.4 show respectivelya diagram; and curves Villustrating .the construction and operation of apparatus shown in Figs. 1 and 2.

The cathode ray .electrostatic recording and reproducing devices employed inthe system, of 5; the invention may be of the general type disclosed inthe copending patentapplicationof R,.R...l,iesz,v and H. S. Wertz, Serial No.145,442, ledMay29, 193.7.v 'Briefly describedthe cathode rayndeyicey disclosed in that application .comprises an evacuj ated enclosure dividedinto two compartments vfor. chambers .by a plate or'disc of insulating material Whichin'cludes a number of elements in the form of plugs; iineA Wires or cylinders of ametal lic.l conducting material, insulated from V,each f5. other, Vextending throughtheLdisc perpendicular. toits `plane and'arranged in,'aY circle ,nearvthe periphery of the disc, acting as atargetfor elec'- tron beams produced by angelectron gunmechanism ineach chamber moving in a .circular path over the respective ends of the metallic plugs... The electron beam in one..chamber, whichis modulated by signals toberecorded,V inpassage over.' the ends of .the plugs places electrostatic charges thereon which yare proportional; to` the signal variations. The velectron A,beam ir 1,jtheother chamber, which is arranged to movein synchronism .but ,iny an Vout-.of-pliaserelationship with the recordingbeam, by secondary emission action removes the charges previously'placed on [the Aplugs in the target u,bythe recording beam. y

' .A c,cndp. ctingring in the .reproducinghchamber collects thesecondary-'electrons from the target' in- ,this process, .the y rato 0f. emissie. dpffnfiiig" 'I uponthe kCharges sc ,that the lltuetfngf; 'me secondary emission Vcurrent v inf the conductingringwillbe a copy of the signal Waves modulating thefrecording beam. v. n, The use of such cathode'ray devicesto accomplish-the purposes of the invention requires 'modification of Vthe targetWithn each.` 'cai'.lfiodeA ray tube Aand"modification of 'the control circuits exterior to the tubes for controlling the deflection j of VtheV electron beams'within the tubes'.`

. I The modification of the target in each cathode 45A ray l' device" land A'thef' recording and reproducing process in accordance with theV present invention l are illustrated diagrammatically in Fig. 3 which Fig. 3, as in the case of the target villustrated in Figs.1" and2 of the aforementioned copendingpatent application, the target-.consists of a circular plate or disc I3 of insulating `material and at row of plugs or Wires 46. of conducting material, insulated from each other, extending through 55 the insulating disc perpendicular to the plane thereof, spaced around an inner circle (of average radius r1). In addition, the target I3 includes an outer ring I of (metallic) conducting material of average radius r2, which may be connected to the metal ring 45 surrounding the target I3, as shown in Fig. 1, and which is separated from the inner circular row of metal plugs 46 by the insulating material of the disc I3.

For each .cathode ray tube used, the electron beam deflecting circuits to be described in connection with Figs. 1 and 2, which control the electron gun mechanism in the recording and reproducing chambers, are designed to make the electron beam in either the recording or the reproducing chamber traverse at a given angular velocity altenately the circular path ABC of radius r1 and the circular path DEF of larger radius r2 on the face of the target in that chamber, and to make the electron beam in the other chamber of the tube traverse at a different angular vvelocity a circular path of radius r1, equivalent to the circular path ABC', on the opposite face of the target in the latter chamber, continuously.

In the case Where the electron beam in the recording chamber traverses alternately the circular paths ABC and DEF on the target, it is effective during the time intervals only in which it moves over the path ABC to place electrostatic `charges on the ends of the plugs 46 in that chamber, to make an electrostatic record of the signal variations modulating the beam during those time intervals, but is ineifective to make any electrostatic record during the alternate equal time intervals in which it is passing over the circular path DEF, because it then impinges on the conducting ring I. Thus the portions of the signal variations modulating the beam during these latter time intervals are effectively eliminated. For that case, the electron beam in the reproducing chamber continuously traverses the equivalent circular path ABC over the other ends of the plugs 46 in the latter chamber, but with an angular velocity equal to one-half that of the recording beam, and reproduces the electrostatic record of signal variations previously placed on these plugs by the recording beam during the alternate time intervals in which it passes over the -path ABC, in the manner described in detail in the aforementioned copending patent application. Conversely, when the electron beam in the recording chamber continuously traverses the path ABC on the face of the target in that chamber, it makes a continuous electrostatic record von lthe plugs 46 of the signal variations modulating the recording beam during each revolution, and the delayed beam in the reproducing chamber alternately traverses the circular paths ABC and DEF with an angular velocity which is twice that of the recording beam so that those signal variations recorded on the plugs 46 are reproduced in alternate revolutions of the recording beam.

In a preferred embodiment of the signaling system of the invention illustrated in Figs. 1 and 2, the beam delecting circuits associated with the single cathode ray tube I0, employed at the sending station of Fig. 1, are designed to make the recording beam alternately traverse the circular-paths ABC and DEF on one side of the target in a time of second for each revolution, Where f is the fundamental frequency produced by the controlling harmonic producing oscillator and is equal to the fundamental frequency of the signal Wave or an integral submultiple thereof, and to make the reproducing beam continuously traverse an equivalent circular path ABC on the reproducing side of the target in a time of second, that is, in twice the time that the recording beam traverses the equivalent path, and the l beam deilecting circuits associated with each of the two cathode ray devices III) and 2I0 at the receiving station of Fig, 2 are designed to make the recording beam continuously traverse the circular path ABC in a time of second for each revolution and to make the reproducing beam alternately traverse the equivalent circular path ABC and the path DEF on the other side of the target in a time of second for each revolution, that is, in one-half the time taken by the recording beam at the reproducing end.

Referring to Fig. -1, the electron beam deflecting circuits for controlling the electron gun mechanisms in the recording and reproducing chambers of the single cathode ray tube I0 include an oscillator, indicated by the box 3, which may be of any of the well-known types for producing an alternating current sine wave of a given fundamental frequency f. The output of the oscillator 3 is connected in parallel to the inputs of three control circuits 4, 5 and 6.

The control circuit 4 includes in order fullwave rectifier 1, the selective circuit 8, a resistance loss `pad 9 of fixed value, a phase splitting network 20 consisting of the condenser 2l and resistance 22 in series shunting the branch circuit 4, and two equivalent parallel branch circuits 4 and 4, respectively connected across the condenser 2! and the resistance 22 of the phase splitting network 26. The branch circuit 4 comprises in order the bufferamplier 23 of high input impedance, the variable loss pad 24, the resistance loss pad 25 of fixed value, the amplier 26 and the shunt resistance 2l connected across the output of ampliiier 26, the terminals of the resistance 21 being connected across one pair of deflecting plates 58 of the electron'gun mechanism in the recording chamber II of the cathode ray device I6. Similarly, the branch circuit 4 comprises in order the buier amplifier 28, the variable loss pad 2S, the resistance loss pad 30 of fixed value, the amplier 3l and the shunt resistance 32 the terminals of which are connected across the other pair of deecting plates 59 of the electron gunmechanism in the recording chamberll of the cathode ray device.

Each of the variable loss pads 24 and 29 consists of four copper-oxide rectifier units connected in a balanced bridge circuit, one diagonal AB of each bridge circuit being .connected across the branch circuit 4 or'4.

The copper-oxide units in the pads 24, 29 are so poled that when biasing current from the ampliiiers 34, 35 is supplied so as to `flow from C tov D, the copper-oxide rectifier units provide a per-oxide rectiers in .these bridge circuits so as to change .t-he loss provided thereby in .the branch circuits 4, 4, between high and low values so that the amplitudes of the :currents 90 degrees out `of phase passing to the lampliers "26 and 3I in branch circuits 4 and 4", respectively, lchange every cycle between the values a1 and a2 as shown in the curves of Fig. 4m) and Fig. 4(5). The particular phase at which the change in amplitude takes place determines the point on the circumference of the circular path ABC traced by the recording electron beam at which the radius changes from r1 to r2, as indicated in Fig. 3. To obtain the required operation of the modulators 24 and 29 it is necessary that the amplitude `of the voltages applied across the diag- -ona-l AB thereof from .the output of the ampliers 23 and 28, respectively, be small compared with 'the amplitude of the square-topped Waves supplied to the diagonals CD of the modulator ybridges from the output of Iampliers 34 and 35. This can be obtained by suitable selection of .the impedance values yof the apparatus in the circuits 4 and 5, and lby suitably adjusting the gain of the ampliers.

rl`-he vol-tages required to be applied to the pairs I, 52 of deiiecting plates in the yreproducing chamber I2 of the cathode ray tube IIl to cause the reproducing electron beam to continuously trace a circular path of radius T1, over the ends of metallic plugs 46, on the reproducing side of the target I3, in a time of per revolution, and with the proper synchronized phase relation with respect to the Irecording electron beam in the recording chamber to re-produce the recorded signal variations, are derived from the wave of fundamental frequency f generated by the oscillator 3 in the following manner.

A sine Wave of the frequency f is transmitted by the oscillator 3 into the branch circuit 6 in which it is amplified by the amplifier The amplified waves pass through the phase shifter 3i, which is adjusted to give the required lag in the voltage Wave transmitted through branch circuit 6 behind the voltage Wave transmitted through lcontrol branch circuit 4, so that, .reierring to Fig. 3, the reproducing electron beam begins to traverse its circular path ABC over the plugs 45 on the reproducing side of the target at the same insta-nt the recording beam starts to traverse its circular path ABC on the recording side of the target, both beams rotating in the same direction. The output of the phase shifter Si is impressed on the phase splitting network 38 which operates to split the applied Voltage Wave into two components 90 degrees out cf phase, one component taken oi from the terminals of the condenser 39 bei-ng applied across the pair 5i of deflecting plates, and the other component taken off across the terminals of the resi-stance 4I being :applied across the other pair of deecting plates 52 of the electron gun mechanism in the reproducing chamber.

The effect of the recording electron beam, traversing at a time per revolution of second alternately the active circular path ABC and the inactive circular path DEF on the target I3 under control of the voltages applied to the delecting plates in the recording chamber inthe manner described, is to split up the signals modulating the beam into equal elements on a time basis, alternate elements of which (those modulating the beam in the time intervals in which it traversesV path DEF' over conducting ring I) are discarded, and the remaining alternate elements being electrostatically recorded on the plugs 46 in the path ABC of the beam. The eiect of the reproducing beam traversing, under control of the voltages applied to the deecting plates in the reproducing chamber as described, the active circular path ABC over ther other ends of the plugs 46, continuously with an angular velocity 1? second per revolution) which is half that of the recording beam, is that the recorded signal elements will be reproduced in such manner that they are stretched out toY twice their original duration each occupying the same time interval formerly occupied by it and the succeeding discarded signal segment.

The reproduced signal elements collected by the collecting electrode 6D are impressed across the resistance 43 on the input circuit of the vacuum tube amplifier 44 and the amplified signal elements, which now occupy only one-half the total signal frequency range formerly occupied by the original signals impressed on the DI terminal of the cathode ray device I0, are transmitted over the transmission line L to the receiving station illustrated in Fig. 2.

In the receiving station of Fig. 2, two cathode ray tubes IIO, ZID, shown diagrammatically because each is identical. With the device III employed at the sending station, are used for rst recording and then reproducing the signal elements received over the line L. Two cathode ray devices are employed because it is desired to reproduce each signal element twice in order to ll the Agaps which would otherwise occur in the reproduced signals due to the fact that each alternate signal element or interval was eliminated at the sending station.

The incoming distorted signal elements are amplified by the amplier 41 and portions of the ampled waves are diverted into the parallel circuits 48 and 49. 'Ihese portions of the waves are respectively applied between the modulating element and the cathode element (not shown) of the cathode ray tubes III] and 2I0 by input circuits (not shown) similar to that employed with the cathode ray tube I0 at the sending station, to modulate the intensity of the electron beam generated by the electron gun mechanism in the recording chamber of each tube in accordance With the variations in the applied signal elements.

It is desired to have the recording electron beam in each of the tubes I Il, 2I0 continuously trace out a circular path ABC of radius r1 over the ends of the conducting plugs in the circular row on the target in the recording chamber with a frequency f or a time of revolution of second, in order to have each beam make a continuous electrostatic record which is an exact copy of the incoming signal segments reproduced in the reproducing chamber I2 of the cathode ray device I0 at the sending station. Therefore, an electron beam deflection control circuit 60 including in order an amplifier, a phase shifter and a phase splitting network, identical with the control branch circuit 6 associated with the repro- :.ducingdeflection platesv of the cathode ray tube, 1I-.0'atthe sending station,is used for deriving the requiredvoltages 9 0' degrees out of phase applied ,to the two. pairs of deflection plates (not shown) in'therecording chamber of each of the tubes It is desired that the' electron beam generated inthe' reproducing chamberof eachof the .tubes .110; 2I0'operates ,to cause all of the signal eleizo vmentsrecorded on' the conducting plugs 46 while the recording beam traces the circular path ABC,

tofberreproduced'but in atime of c 2f 5- y second per revolution.- As the recordlng'is "done lin'atirneof 1' l second per revolution, it isv apparent that the -value of veach frequency in the reproduced sigln'al 1 elements in that case would be double the .value as recorded, Whichwould mean that all of the frequencies in 'the reproduced signal segment are restored to thevalues they had origi- 'second per' revolution the circular path ABCrover 'the plugs' V46 on the target in which interval it nally at the sending station.

f 'Ihis isi accomplished `by employing for controlling the deflection voltages applied to the pairs of deecting plates in theA reproducing chamber .ofreach tube, thecircuits 40 and `50, lthe elements in the control circuits for each tube being identical withthose in the control circuits 4 and 5 employed for controlling the recording operation in the similar tube I0'at the sending station, so that -.the reproducing electron'beam in each tube ||0, 2 I I lalternately traversesin the time of is effective to reproduce the recorded signal variations, and the circular path DEF over the conductingfring I of the target in'which interval it is not effective-to reproduce anything.

The control circuit 4|]` associated with the re- I 'producing deecting plates of the tubes IIO and 2I0, as indicated, comprises a full-wave rectifier I0 for rectifying the sine wave of fundamental frequency f supplied bythe oscillator 300, simicomprises the overloaded amplifier |40 for changin g the'sne wave of frequency f received-from the oscillator300 toa square-topped wave of the same frequency, which is applied in .parallel Athrough amplifiers to properly bias variable loss vpads within the `boxes N1 and N2, respectively,

corresponding tothe 'amplifiers 34 and -35 and fthe? copper-oxide" rectifier bridges 24 and 29 'manner similar to that described for the similar within the box N in` Fig. 1.

The -control circuits 40 and 50 operate in a I `circuits 4'and '.'l` of Fig. l to make the deflection LAvoltages applied to the reproducing plates of the 'tubes y| I0, A2I0 such that the reproducing elecltron beam` `in-each tube alternately traverses the `circular pathsgABC and-DEFin alternate time.

intervals of 1 2f l second each sothat it vwill reproduce in ,transmission over the "path'ABC all the signal segments previously recorded on the'plugs 46' by-the l vrecording beams but with 4each frequencytherein doubled so that it is restoredl tothe value it originally had at thev sending station.

lThe connection between the loverloaded amplilier |40 and the circuits within the box N2 only are crossed, as indicated,[.to `cause the squaretopped control wave to be applied 180 degrees out of phase to the variable loss pads in circuitsv N1 and N2 respectively, sci-that. eachtube ||0 and 2|0 reproduces the same signal segments for alternate time intervalsv lasting second each, f

The reproduced signal segments Yare taken off from the reproducing chamber of the cathode ray tube I I0 by an outgoing circuit includingk an amplifier 90, and the alternatereproduced signal' segments are taken off from the'urep'roducing chamber of the'catho'de ray tube 2I0 by an outgoing .circuit including an amplifier |00,y in a manner similartothat described for the cathodel ray tube I0v at the sending station of Fig. 1, and the amplified signal segments, rthel frequencies of which are now increased to the original values which they had at the `input of the cathode ray Y,

tube I0 at the sendingrstation of Fig 1, arecom'- bined in a common circuitl |30 leading to 'a suit- 'able receiving device |20 asindicated. The rsignaling wave impressed on the receivingr signaling device |20 will contain only the alternate speech segments vrecorded at the sending stati'o`n',.butt4 1 each 'of these'segments is reproduced twice consecutivelyso that the signals'asreproduced by the receiving'device Y|20 will contain no's'ilent gaps. v Y

quency f lreceived from the oscillator 3 at the v sending station and the'- oscillator 300 atv the receiving station is preferably made adjustable vby any suitablemeans so that the relative points inn vthe cycle at which the speech wavesv are f f, switched or interrupted are the sam'e at the sending and'receiv'ing ends of the system. l

In a modication of the circuit illustrated and described, the"y fundamental frequency f, determining the rate at which the speech or other signal wave of slowly varying fundamental fre-- quency' and Wave shape is 'chopped' up, mayv be of a' speakersvoice instead of being generated by the auxiliaryoscillatorsS-"and 300 as described.I

In an unvoiced sound, where the voicehas no nite fundamental frequency, the rate of in- It isi apparent that the amount of reduction in vderived directly from the fundamental frequency v ',terruption may be determined by an oscillator.. having Vthe average frequency of the speaker's voice. f

the lfrequency rangeof the signals transmitted inl a system, such as described, may be made any desired fraction of the original frequency range ployed at the receiving station and utilizing different harmonics ofthe frequency f to control the deflection voltages of the single cathode ray "tube `at the sending station.- Where a frequency 'reduction v'of 2 tov 1 is' desired, two cathode rayk The phase of the Wave of fundamental fre by Varying the number of cathode ray tubes em- T79 'tubes-operating in alternation would be employed at the receiving station and the harmonic 2f would be selected by selective circuit 8, as indicated. Where a reduction of 3 to 1 is required, three cathode ray tubes operating in sequence would beA employed at the receiving station and the harmonic 3f would be selected at the sending station, and Where a 4 to 1 reduction is desired, four cathode ray tubesoperating in sequence would 'be employedand the harmonic 4f would be selected at the sending station, and so on. However, in the case where an odd harmonic is required to be selected by the selective circuit at the sending station, the full wave rectifier 'l would be eliminated.

Other modifications of the circuits which have been illustrated and described which are within the spirit and scope of the invention will be apparent to persons skilled in the art.

What is claimed is:

l. A method of changing the form of a message wave, which consists in chopping it up into a number of segmentsY on a time basis, discarding certain segments, electrostatically recording the remaining segments at a given speed, and reproducing the recorded message segments at a lower speed, whereby the total frequency range occupied by the reproduced message components is reduced.

2. The method of reducing the width of the frequency band required for transmitting an alternating current signal wave, which consists in chopping up the wave into a plurality of small portions on a time basis, eliminating certain of said portions, electrostatically recording the remaining portions at a given speed, reproducing the recorded portions of the signal waves at a lower speed whereby each frequency in the reproduced signal portions lis reduced to a fraction of its original value, transmitting the reproduced signals so modified over a transmission medium, and restoring the frequencies of the transmitted wave to their original values at a receiving point.

3. The method of reducing the frequency range required for transmitting an alternating current signal wave, which consists in chopping up the wave into a plurality of small intervals on a time basis, eliminating alternate intervals, electrostatically recording the remaining intervals of said waves at a given time rate, reproducing the recorded intervals at half the speed of recording, whereby the duration of each interval is stretched out by a factor of two and the total frequency range occupied by the reproduced signal intervals is halved, transmitting the reproduced signals so modied over a transmission medium, and at a receiving point electrostatically recording the received signals at the same speed as received, and reproducing the recorded signals at twice the speed of recording whereby the frequency components therein are restored to their original values.

4. A frequency changing system comprising means for generating an alternating current signal wave containing a wide range of frequencies, a cathode ray device for producing an electrostatic record'of separated portions of said wave on a time basis while discarding the intervening portions, and for reproducing the recorded portions at such a time rate compared to the speed of recording that the value of each frequency of the reproduced waves bears a desired ratio to its original value.

5. The method of communication which consists in chopping up an alternating current m65,-

sage wave into a large number of small fragments on a time basis, selecting a sufficient number of said' fragments to insure intelligibility of the message when the fragments are reproduced, while eliminating the remaining fragments, electrostatically recording the selected fragments at a given speed, reproducing the fragments at a lower speed such that each frequency therein' and the total frequency range occupied by each fragment is reduced by a desired amount, transmitting the reproduced message fragments and at a receiving point 1 electrostatically recording the received fragment at the same speed as received, and reproducing the resulting record at such speed as to restore the message components to their original frequency value.

6. A frequency reducing system comprising a source of alternating current signal waves of a wide range of frequencies, means to chop up the wave produced by said source into a plurality of small equal portions ona time basis, means to produce an electrostaticl record of every alternate portion of said waves while discarding the intermediate portions, and means to reproduce the recordedfportions at such a time rate that each frequency therein is reduced to a desired fraction of its original value, whereby the total frequency range of said signal waves is effectively compressed.

7. The system of claim 6, in which the recording and reproducing means comprise a single cathode ray device.

8. In a communication system comprising a sending and a receiving station connected by a signal transmission medium, said sending station comprising a source of signal Waves comprising a wide band of frequencies, a cathod ray device for producing an electrostatic record of portions of said waves spaced apart with respect to time while discarding the intermediate portions of the waves, means for reproducing said record at a slower rate than the recording rate todecrease the signal frequencies from their original values, and` means to transmit the reproduced signals to said` medium, said receiving station comprising means for reproducing the portions of thel signal wavesreceived overi said medium in such manner as to restore the frequencies therein to their original values.

9. A communication system comprising a sendingstation and a receiving station joined by a signal transmission medium, said transmitting station comprising a source of alternating current signal waves, means for eliminating separated portions of the signalon a time scale and for electrostatically recording the intermediate portions, and means for reproducing and transmitting to said medium the recorded portions in such manner that each successive transmitted signal portion is stretched out so that it occupies the time intervalv formerly occupied by it and the succeeding eliminated portion together, said receiving station comprising means for restoring the modied signal portions received over said medium to their normal time intervals, and means for replacing each signal portion eliminated at thetransmitting station with a copy of thel preceding retained signal portion so that the nal signal wave is continuous;

10. A communication system comprising at a transmitting station a. complex wave message source, means for eliminating alternate time intervals of the message wave received from said source and retaining other intervals, means for electrostatically recording the retained portions of the message and means for reproducing and transmitting to a receiving station the recorded portions at a rate different `from the recording rate, and means at said receivingy station for restoring the transmitted portions to their normal time intervals. y

11. `T'he system ofclaim 6 in which the chop-v ping up, recording and reproducing means comprises alsingle cathode ray device comprising an evacuated enclosure divided into tWo chambers v each containing an electron beam generating apparatus,` separated by a target consisting of a disc including a ring of conducting material and a parallel circular row of small plugs of conducting material insulated from each other, extending through the target perpendicular to its plane, separated from said ring by insulating material,

y f means to modulate the intensity of the beam generated in one chamber with said alternating current signal wages, means to cause the latterfbeam to'revolve at a given angular velocity alternately in circular paths over the ends 'of said *plugs inf said one chambento make an electrostatic record of the signal variations modulating the beam durv ing that interval, and over said conducting ring, the signal variations modulating the beams during the alternate time intervals in which it moves yover the conducting ring being thereby elimihated, means to cause the electron beam generatedvin the other chamber to revolve at a lower angular velocity and with the required delaynwith 10 to its original valueand the total frequency range occupied by the reproduced signals being less than that of the original signals;

YROBERT R. RIESZ. 

